A century of research of existing thermodynamic cycles has developed piston engines exceeding 40% efficiency and open cycle gas turbine engines approaching 30% practical efficiency. A breakthrough engine concept has been invented by Dr. Michael Wilson (US Patents 5,966,927 and 6,105,359) and is called the TurbXT?M engine. This new engine, operating on the Atkinson cycle, can theoretically increase engine performance and fuel economy, and reduce emissions as compared to the open cycle gas turbine. The TurbXT?M engine implements a constant volume, continuous combustion process in rotating turbo-machinery. Based on a theoretically ideal thermodynamic analysis, this novel innovation will always have a higher thermal efficiency than a typical gas turbine at the same compression ratio. This particular concept has the inherent capability of easily varying the load with very simple controls. The purpose of this study was to determine experimentally the non-fueled or "air driven" performance characteristics of the prototype TurbXT?M engine. The results of this study will be presented and discussed. Results of loaded tests indicate that with lower gap settings the engine has negative torque-speed characteristics similar to those of gas turbine engines. Although air driven tests were limited to combustion chamber pressures of up to 345 kPa, the prototype engine did not produce the anticipated torque values as envisioned by the inventor. Poor torque output was indicative of the excess leakage prevalent across the rotor/stator gap. It is recommended that TurbXT?M design changes should address a better way to control the gap setting between the rotor and two stators, as well address blade angle and expansion passage designs to reduce the losses associated with poor air-incidence angles.